Snap action mechanism



1966 E. B. ANGOLD 3,248,959

SNAP ACTION MECHANISM Filed Sept. 20, 1965 United States Patent 3,243,959 SNAP ACTION MECHANISM Edward Barnabas Angold, Westbonrne, Emsworth, England, assignor to Plessey U.K. Limited, a British company Filed Sept. 20, 1963, Ser. No. 311,284 9 Claims. (Cl. 74100) This invention relates to snap action mechanisms primarily for electric switches.

It is an object of the present invention to provide a snap action switch mechanism which is capable of undergoing a large number of switching operations.

A further object of the present invention is to provide a switch mechanism whereby the inertia of the movable parts of the switch is kept as low as possible.

A first aspect of the invention provides a snap action mechanism comprising an arm mounted for pivotal movement between first and second stop positions, a link pivotally connected to the arm at a location spaced from the pivot of the arm and a compression spring adapted to tension the link in such manner that upon producing relative movement between the arm and link to cause the line of action of the tension force in the link to pass through the pivot axis of the arm the latter is caused to move from one stop position to the other with a snap action.

A second aspect of the invention provides a snap action mechanism, including an arm mounted for pivotal movement between first and second stop positions, a link pivotally connected to the arm at a location spaced from the pivot axis of the arm, and a leaf spring having one end pivotally mounted in a support and its other end pivotally connected to the link in such manner that the leaf spring is maintained under compression and the link under-tension, the arragernent being such that upon producing relative movement between the link and the arm to cause the line of action of the tension force in the link to pass through the pivot axis of the arm the latter is caused to move with a snap action from one stop position to the other.

Preferably the mechanism is actuated by providing an actuator member which is arranged to displace the connection between the link and spring, so that the connection is moved from a position to one side of a plane containing the pivot axis of the movable arm to the other side of this plane.

For a better understanding of the invention reference will be made to the drawing accompanying the provisional specification which is an elevation of a snap action mechanism adapted to act as an electric switch, and to the accompanying drawing which is an elevation of an electric switch incorporating a snap action according to the invention; for convenience this figure is identified as FIGURE 2 and the provisional specification drawing as FIGURE 1.

The electric switch includes a generally rectangular housing 1 moulded from a suitable plastic material, the housing having a base 2, and side walls 3. The housing has a cover (not shown) which is intended to close off the interior of the housing. The housing 1 and the cover have diametrically opposed holes 4 through which may pass means for attaching the switch to a support or mounting.

The snap action mechanism includes a fixed mounting member or support 5 which is rigidly secured to the housing 1, by means of a tongue 6 which engages a recess 7 in the wall 3 of the honing and a portion 8 which engages a through slot in the wall 3 of the housing, to provide a projecting part 9 which is adapted to act as the common terminal for the switch.

Two substantially right angled bends 10 and 11 are formed in that part of the member 5 which is located "ice inside the housing. A transverse V-shaped groove 12 is formed in the inside of the bend 11, the groove 12 forming a fixed fulcrum for the end 13 of an arm 14 carrying electrical contacts 15A, 1513. The end 13 of the arm 14 is cranked as shown at 16.

The angular pivotal movement of the arm 14 is limited by stops 17A and 17B which conveniently but not essentially serve as electrical contacts. In the case shown when the stops 17A and 17B serve as contacts, they are mounted on metallic pieces 18 mounted on the wall 3 of the housing 1 and which project out from the housing to act as terminal means.

A short through slot 19 is formed in the member 5 at the bend 10. The slot 19 is engaged by the shaped end 20 of a leaf spring 21. The leaf spring 21 is maintained under compression, in the bow shape illustrated, by a link 22 which is connected at one end 23 to the other end 24 of the leaf spring, and at its other end 25 to the movable arm 14 at a location spaced from the pivoted end 13.

The connection between the link end 23 and the leaf spring is constituted by a hole 26 in the leaf spring which is engaged by the link and an enlarged head 27 formed at the end of the link.

The other end 25 of the link is shaped to form a hook which engages with a hole 28 in the arm 14. The portion of the member 5 from the bend 11 to a convenient location adjacent to the bend 10 is slotted to accommodate the link 22. In addition, the end part 13 of the arm 14 is bifurcated to facilitate relative movement between the arm and the link. Conveniently the arm 4 has a relatively long body part to one end of which the contacts 15A and 15B are fixed. The other end of the body part separates into two diverging portions the ends of which pivotally co-act with the groove 12.

The end 24 of the spring 21 co-operates with a plunger type switch actuator member 28A slidably mounted in the wall 3 of the housing. The end 24 bears against the inclined surface 2813 at the upper end of the plunger 28. The provision of the inclined surface 28B ensures that the end of the spring is able to move relative thereto without digging-in. The slope furthermore avoids undue loss of spring energy and assists in increasing the efiiciency of the transfer of spring energy to the movable arm 14.

The wall 3 is cut away to provide a recess 29 which makes it possible to use a relatively lengthy leaf spring 21, a part of the bow of the spring 21 entering the recess.

The relative positioning and dimensioning of the spring 21, the link 22, the arm 14 and the pivot points at 12 and 20 are chosen such that the pivotal connection between the link 22 and the arm 14, the pivotal connection between spring 21 and the link 22 and the pivot point of the leaf spring lie in the member 5 define the corners of a triangle (identified as A, B, C in the figure) and such that the projection of the pivot axis between the arm 14 and the groove 12 (the point D) onto the line AC always lies between points A and C. Consequently the compression force in the spring 21 and the tension force in the link 22 produces a resultant component of force which always tends to move the arm 14 in a particular direction. With the arrangement actually shown i.e. with the point B above the line AC, the arm 14 tends to pivot in an anticlockwise direction. The mechanism therefore has a rest position in which the contact 15B abuts the stop 17B and in which the link 22 passes below the fixed pivot point. This position is indicated by the dashed lines in the figure and the points AC are located at A and C.

When the plunger 28A is depressed, that is to the position shown in full lines, the spring 21 is tilted relative to the member 5. During this movement the line AC moves from the rest position indicated by A'C' towards the position illustrated in full lines, and in so doing, passes through a position in which the point D lies on the line AC immediately after passing through this position the tension in the link causes the arm 14 rapidly to move with a snap action in a clockwise direction to cause the contact 15A to abut the contact 17A.

As soon "as the pressure isrernoved from the plunger the major forces in the system are'the'tension forces in the link 22 and the compression forces in theleaf spring 21, so that the resultant force'acts in said predetermined direction to return the arm 14 to its initial position. During this movement the line AC passes through the point D so that the arm once again moves with a snap action.

The switch illustrated in FIGURE 2 is generally similar to that shown in'FIGURE 1. In the circumstances those parts of the two switch constructions, and associated snap action mechanisms which are alike will be identified'by the same reference numerals, and will not be described in detail.

In the embodiment of FIGURE 2 the connection between the spring 21 and the link 22 is different from the other embodiment. The end of the spring is curved, as is shown,'to provide a C-shaped end 30'which bears upon the sloping surface 28B of the plunger 28A.

The end of the link 22 is deformed as is indicated in FIGURE 2 to provide a head part 31 having a curved part 32 which abuts the inside curved surface of the link end 30. This form of contact between the part'32 and the end 30 provides a self centering bearing surface between the abutting parts.

The operation of the switch of FIGURE 2 is similar to the operation of the FIGURE'I construction, and in the circumstances a detailed explanation of the FIGURE 2 arrangement is not thought necessary.

In a modified construction the hnk 22 could be formed integrally with the spring 21, the link being in fact an extension of the strip material used to provide the leaf spring.

What I claim is:

1. A snap action mechanism comprising a rigid arm, knife edge means by which said arm pivots movement between first and second stop positions, a link pivotally connected to the arm at a location spaced from the pivot of the arm and a compression spring connected to and adapted to tension -the link in such manner that upon producing relative movement between the arm and the link to cause the line of action of the tension force in the link to pass through the pivot axis of the arm the latter is caused to move from one stop position to the other with a snap action.

2. A snap action mechanism includinga rigid arm including knife edge means for pivot movement of said arm between first and second stop positions, a link pivotally connected to the arm at a location spaced from the pivot axis of the arm, and a leaf spring separate from said arm and having one end pivotally mounted in a support-and its other end pivotally connected to the link in such manner that the leaf spring is maintained under compression and thelink under tension, the arrangement being such that upon producing relative movement between the link and the arm to cause the line of action of the tension force in the link to pass through the pivot axis of the arm the latter is caused to move with a snap action from one stop position to the other.

3. A snap action mechanism comprising a support element, first and second stop means positionally fixed relative to he support element a rigid arm including knife edge pivot means for pivoting the arm on the support element for movement of the arm between the first and second stop means, a link having a first end pivotally connected to the arm at a location spaced from the pivoted region thereof, a compression spring separate from the arm adapted to tension the'link, the spring operatively engaging with the link in such position that the pivotal axis of the arm is intermediate the connection between the link and arm and the connection between the link and spring, and in such manner that upon producing relative movement between the link and arm which causes the line of action of the tension in the link to pass through the .pivot axis of the arm, the latter is caused to move with a snap action from one stop position to the other.

-4. A snap action mechanism as claimed in claim 1, comprising an actuator member which on movement in a predetermined direction relative to the support is arranged to displace the connection between'the link and spring relative to thepivotal axis of the arm in such manner that said line of action is caused to move through the pivotal axis of the arm.

5. A snap actionmechanism as claimed in claim 2, wherein one end of the leaf spring is shaped to provide a curved surface which-contacts with an abutment surface 25.

wherein-said abutment surface is a plane surface which is inclined to thedirection of an operational movement of the actuator member, and-wherein the inclination of the surface is such as tofacilitate relative movement between 'thesaid other spring end and the abutment surface.

7. A snap action mechanism as claimed in claim 2, wherein the other end of the link is deformed to produce ahead element which provides said pivotal connection between the spring and the link.

8. A snap action mechanism as claimed in claim 7, wherein an end of the link is deformed to provide an arcuate abutment part which co-operates with the leaf spring to provide a self-centering bearing surface between the link and spring.

'9. A snap action'electric switch'comprising a rigid arm, a moving contact carried by said arm, knife edge pivot means by which said arm pivots for movement between first and second stop positions, first and second fixed contacts at said positions, a link pivotally connected to the arm at a location spaced from the pivot of the arm anda compressionspring connected to and adapted to tension the link in such manner that upon producing relative References Cited by the Examiner UNITED STATES PATENTS 2,413,130 12/ 1946 Aitken 20067 2,452,425 l0/1948 Berkholder 20067 2,486,033 10/1949 Kaminky 74-100 X 2,505,605 4/1950 Coake 74-100 X 2,809,247 10/ 1957 Wintle 20067 MILTON KAUFMAN, Primary Examiner.

BROUGHTON G. DURHAM, Examiner.

F. E. BAKER, Assistant Examiner. 

1. A SNAP ACTION MECHANISM COMPRISING A RIGID ARM, KNIFE EDGE MEANS BY WHICH SAID ARM PIVOTS MOVEMENT BETWEEN FIRST AND SECOND STOP POSITIONS, A LINK PIVOTALLY CONNECTED TO THE ARM AT A LOCATION SPACED FROM THE PIVOT OF THE ARM AND A COMPRESSION SPRING CONNECTED TO AND ADAPTED TO TENSION THE LINK IN SUCH MANNER THAT UPON PRODUCING RELATIVE MOVEMENT BETWEEN THE ARM AND THE LINK TO CAUSE THE LINE OF ACTION OF THE TENSION FORCE IN THE LINK TO PASS THROUGH THE PIVOT AXIS OF THE ARM THE LATTER IS CAUSED TO MOVE TFROM ONE STOP POSITION TO THE OTHER WITH A SNAP ACTION.. 